Aero gas turbine engines are very high speed thermodynamic machines burning jet fuel for combustion with the high speed exhaust effluent (2500 to 3000 ft./sec.) impinging on turbine blades, rotating them, and torque transferred with mechanical drive transmissions at the center of the engine, defined as several shafts or spools, running one inside the other. No design nor innovation has been conducted on utilizing knowledge and the art of magnetic transmissions that operate at high speed to benefit the efficiency of aero gas turbine engines or differing power propulsion architecture. The requirements to segment rotating machinery in order to provide a multitude of gearing, or gear ratios to extract 100% efficiency from a rotating machine (electrical or otherwise), in particular a aero gas turbine engine machines which have broad need for improvement of thermodynamic and aerodynamic efficiencies, this has not been done before.
The topology today of mechanically linked gas turbines to connect the bypass fan to compressor to the power turbine is very limited as all the stages of the compressor are connected together to one spool or more which is connected to the power turbine, hence driving the compressor. If the stages of the bypass fan and compressor could be individually segmented from each other, and subsequently from the power turbine, and the power turbine stages segmented also, dramatic increases in thrust and efficiency are possible, as then all the desired stages of the gas turbine can be run at the optimal speed for mass flow air velocity, temperature, air density (altitude) and flight Mach number.
There have been numerous investigations on analysis and scaling of electrical machines as it relates to DC synchronous permanent magnet motors and generators, but little to no analysis or criteria for defining architectures and topology of electrical machines known as magnetic gears or magnetic transmissions. The analysis of magnetic force and torque density has been addressed by a number of investigators, but very little on high speed transmission machines has been conducted, and almost the complete lack of this type of analysis, and hence promotion of control technologies does not exist.
Initially, papers have focused mainly on the calculation of the torque as the output of a rotating body in electrical machines, but nothing as with a stator and a rotor in an aero gas turbine. In the past researchers have drawn comparisons on several different methods to calculate the torque density and transmission of power. These efforts resulted in torque density calculation at several different locations along the baseline of an experimental three-phase stator and rotor permanent magnet synchronous electrical machine demonstrating a quasi-static magnetic field for example, but this was not a high speed machine nor had the need for a variable torque in moderating the transfer of power. No application has ever been done in defining innovative topologies for an electromagnetic segmented high torque density aero gas turbine engine transmission, nor defining operability requirements which drive design and topology of the electromagnetic structures.
The problem of magnetically generated vibrations is known and been discussed in research with comprehensive analysis. These vibrations can disrupt the magnetic fields generated, and exist in simple machine architectures using permanent magnets in the rotor and induction coils in the stator, being addressed in numerous cases. In high power density electrical permanent magnet machines, particularly with innovative architectures to increase torque density through volume and surface area, these magnetic phenomena have to be addressed more so when there is the requirement of a multitude of generated magnetic fields and individual torque densities must be maintained and controlled stage to stage in line down the length of a magnetic transmission.
Since the magnetic force increases approximately with the square of magnetic flux, the forces arising from machine designs, motors, generators or gear magnetic transmissions, using rare earth magnets are significantly greater than those from conventional magnet designs. Vibration problems are particularly serious in the machine transmission design when the forcing frequencies match one or more of the structural resonant frequencies in the machine.
Accordingly, a need exists for a very high torque density magnetic topology which will reduce structural resonant frequencies at high revolutionary speeds and address the manipulation of magnetic flux, its direction and magnitude across the air gap and utilize the power of eddy current forces to control transmission ratio.